The present invention relates to a safety net system for construction sites to prevent injury caused by falling debris. More particularly, it relates to a safety net which is extended outwardly at the perimeter of a building or the like by a system of poles and brackets secured to the building.
In the construction of high-rise structures, particularly those in proximity to population centers, it is vital that a system be in place whereby passersby and workmen below will be protected from falling construction debris. In fact, the presence of such systems is required under the law of most municipalities. Typical systems in use today generally include a series of brackets secured to the perimeter of a lower constructed floor or support columns. Each bracket holds a pole which extends upward and outward from the building edge. A safety net, attached at one end to an upper floor, is draped and secured to the extending ends of the poles. The safety net system then in place is extended to catch and retain debris which may fall, roll or be blown off the building during the construction of higher floors.
One prior art system presently in use employs a rocker bracket assembly with a sleeve for receiving the pole. The sleeve is attached to a vertical plate at an approximately 45.degree. angle, which plate abuts the floor edge when the pole is in the deployed position. Extending inward from the plate is a rocker arm mechanism rotatably secured to the floor plate via a bolt placed through a hole in the rocker unit and through a loop unit extending vertically from the floor plate. The rocker arm mechanism permits the system to be easily pulled inward during assembly and disassembly.
There are, however, potentially dangerous drawbacks to this system. First, the pole and bracket assembly is secured to the structure only by a single bolt. If heavy objects falls into the net, the downward force could possibly cause sufficient torsional strain on the rocker arm mechanism to shear off the retaining bolt.
Another potential danger lies in the rocker arm mechanism itself. Although the vertical plate abuts the floor edge ostensibly to prevent outward rotation of the net system, there is no mechanism to prevent inward rotation. High gusts of wind frequently act upon safety net systems, especially at the upper floors of multi-story buildings. The above-described prior art system is susceptible to a dangerous condition wherein the wind may blow the netting and hence the unrestrained pole-bracket assembly inward towards the building, thus leaving the system in a temporarily undeployed state. At the same time, this same wind may cause debris to blow over the sides of the building.
Another prior art system is disclosed in U.S. Pat. No. 3,949,834 to Nusbaum, in which a socket is rotatably secured to the lower-floor bracket via a single bolt. Before deployment, a single cross-bolt placed outward from the socket retains the socket and pole in the upright position within the bracket. To deploy the system, workmen must remove the cross-bolt, thus permitting the pole to extend outward until it rests against a stop. The cross-bolt is then placed in a second location inward of the first so as to retain the pole in the extended position, secured between the cross-bolt and the stop.
Deployment of this system requires a great deal of time and attention, as workmen must remove the nut and cross-bolt from the first position, allow for extension of the system, then insert and secure the cross-bolt through the holes in the second position. Furthermore, the danger of "shearing off" is also present here, as the torsional strain imparted by a falling object must be borne by a single retaining bolt.
A further drawback results from the rigid deployed state of the system. Under certain conditions, it is possible for a falling object to bounce out of the net owing to the lack of rotational "give" in the way in which the poles are fixed to the lower-floor brackets.